Straczekite is a rare vanadium mineral that forms as thin, brittle, platy crystals in oxidized zones of uranium-vanadium deposits. It is typically identified by its dark, metallic-looking appearance and association with other secondary vanadium minerals in the Colorado Plateau region.
Is this straczekite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch straczekite with a known reference. Straczekite sits at Mohs 1-2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: greenish black.
- 3Read the lusterHold the specimen under a strong light. Luster: greasy.
- 4Match the color rangeCompare against the expected color range: greenish black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, microscopic crystals.
Often confused with
Straczekite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Straczekite leaves greenish black, Navajoite leaves brown; luster reads greasy on Straczekite and adamantine to silky on Navajoite.
How to tell apart: Streak differs, so Straczekite leaves greenish black, Hewettite leaves brownish red; luster reads greasy on Straczekite and silky to adamantine on Hewettite.
Often found alongside straczekite
Minerals reported to co-occur with straczekite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ca,K,Ba)(V⁴⁺,V⁵⁺)₈O₂₀·3H₂O
- Mohs hardness
- 1-2
- Density
- 3.09-3.29 g/cm³
- Colors
- Streak
- Greenish black
- Luster
- Greasy
- Transparency
- Opaque, thin flakes are translucent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, microscopic crystals
- Cleavage
- {100}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An uncommon secondary mineral, in seams in argillaceous gangue, in vanadium-rich alkalic igneous and metamorphosed sedimentary rocks (Wilson Springs, Arkansas, USA)
Where rockhounds find straczekite
Classic worldwide localities
- Wilson Springs (Potash Sulphur Springs) mine, Garland Co., Arkansas, and from the Monument No. 2 mine, Monument Valley, Apache Co., Arizona, USA
Field-hunting tip
Where it forms: An uncommon secondary mineral, in seams in argillaceous gangue, in vanadium-rich alkalic igneous and metamorphosed sedimentary rocks (Wilson Springs, Arkansas, USA). If you start seeing hewettite, duttonite, fervanite in float, you are in the right ground. Typical habit: fibrous, microscopic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
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Find straczekite on the map
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